Such tactical radiocommunications networks are usually PMR (Professional Mobile Radiocommunications) networks of the TETRA (Trans European Trunked Radio) type or TETRAPOL type defined by the TETROPOL manufacturers' forum (http:/www.tetrapol.com) or of the P25 type defined by the Telecommunications Industry Association (TIA) for the Association of Public Safety Communications Officers (APCO). PMR networks are private networks with a high level of security. As a result, they are widely used by public safety services, such as law enforcement agencies. These PMR networks follow the technological development of civilian telecommunications, and sometimes use the same resources as those used by operators' networks (wireless and satellite links, fibre optic transmission, voice and data switching).
When a crisis situation (such as an earthquake or a flood or other) occurs in a particular geographic area, professional or public fixed networks in the area can become totally or partly inoperable. In order to supply public safety departments with resources capable of controlling the crisis situation, professional tactical radiocommunications networks are deployed in the field. Currently, radio access points are deployed by tactical vehicles that support radio base stations, which use the technology of the terminals located in the area of intervention.
However, it may happen that the users of a tactical radiocommunications network wish to access the services offered by another fixed or mobile remote radiocommunications network. In such as case, interoperability is very difficult and a particular protocol must be put in place by an operator between the tactical network and the remote network offering additional services.